Go to options. Now, highlight the sound test (6th choice down on the options menu). Hold Left and press A. Now, at the bottom you will see text that says Soft Dip, and has a bunch of zeros under it. Go down and change the zeros to ones to turn lots of codes on. The first two turn on the secret characters. One of them turns on Master difficulty. The others affect gameplay in weird ways. For example, one makes your BP charge on its own. Another makes it so that specials can be done by just pressing Select + B or A.